Polyphosphonic acids and their pharmaceutically-acceptable salts have been proposed for use in the treatment and prophylaxis of a number of pathological conditions which can affect humans or other mammals and involve calcium and phosphate metabolism. Such conditions may be divided into two broad categories:
1. Conditions which are characterized by anomalous mobilization of calcium and phosphate leading to general or specific bone loss or excessively high calcium and phosphate levels in the fluids of the body. Such conditions are sometimes referred to herein as pathological hard tissue demineralizations.
2. Conditions which cause or result from deposition of calcium and phosphate anomalously in the body. These conditions are sometimes referred to herein as pathological calcifications.
The first category includes osteoporosis, a condition in which bone hard tissue is lost disproportionately to the development of new hard tissue. Marrow and bone spaces become larger, fibrous binding decreases, and compact bone becomes fragile. Osteoporosis can be subclassified as menopausal, senile, drug induced (e.g., adrenocorticoid, as can occur in steroid therapy), disease induced (e.g., arthritic and tumor), etc., however, the manifestations are essentially the same. Another condition in the first category is Paget's disease (osteitis deformans). In this disease, dissolution of normal bone occurs which is then haphazardly replaced by soft, poorly mineralized tissue such that the bone becomes deformed from pressures of weight bearing, particularly in the tibia and femur. Hyperparathyroidism, hypercalcemia of malignancy, and osteolytic bone metastases are conditions also included in the first category.
The second category, involving-conditions manifested by anomalous calcium and phosphate deposition, includes myositis ossificans progressive, calcinosis universalis, and such afflictions as arthritis, neuritis, bursitis, tendonitis and other inflammatory conditions which predispose involved tissue to deposition of calcium phosphates.
In particular diphosphonates, like ethane-1-hydroxy-1,1-diphosphonic acid (EHDP), propane-3-amino-1-hydroxy-1,1-diphosphonic acid (APD), and dichloromethane diphosphonic acid (Cl.sub.2 MDP) have been the subject of considerable research efforts in this area. Paget's disease and heterotopic ossification are currently successfully treated with EHDP. The diphosphonates tend to inhibit the resorption of bone tissue, which is beneficial to patients suffering from excessive bone loss. However, EHDP, APD and many other prior art diphosphonates have the propensity of inhibiting bone mineralization when administered at high dosage levels.
The compound risedronate is a more biologically potent diphosphonate compound which can be administered at low dosage levels; these lower dosage levels have resulted in a wider margin of safety and cause little or no mineralization inhibition. It is believed that the decrease in the inhibition of bone mineralization which is exhibited by the low dosage levels occurs because mineralization inhibition is predominately a mass related physiochemical effect, whereas resorption inhibition results from a biological interaction with the cells. In addition, low dosage levels are also desirable to avoid the gastrointestinal discomfort, like nausea, diarrhea, and abdominal pains, which are sometimes associated with the oral administration of disphosphonates.
Despite the low-dosage levels possible with risedronate, the oral administration of the compound sometimes results in patient complaints shortly after dosing; said complaints are usually characterized by the patients as heartburn, esophageal burning, pain and/or difficulty upon swallowing, and/or pain existing behind and/or mid-sternum. It is believed that these complaints originate from esophagitis or esophageal irritation caused by the erosion, ulceration, or other like irritation of the epithelial and mucosal tissues of the upper gastrointestinal tract, generally the mouth through the esophagus, most generally the esophagus. It is hypothesized that said irritation results from the risedronate active ingredient coming in direct contact with those epithelial and mucosal tissues, resulting in the topical irritation thereof.
Accordingly, it became desirable to develop novel oral dosage forms of the risedronate compound which would prevent the release of risedronate compound in the area of said tissues. Said novel oral dosage forms are enteric coated and delay the beginning of the release of risedronate until some point in the small intestine or large intestine is reached and, thereby, provide protection to the tissues of the mouth, pharynx, and esophagus. Said novel enteric-coated oral dosage forms may be in the form of enteric-coated tablets or starch or gelatin capsules containing enteric-coated beads or particles.